1. Field of the Invention
The present invention relates to a fuel cell composed by housing, in a casing, a stack structure formed by stacking a plurality of solid oxide fuel cell units on one another.
2. Description of the Related Art
Heretofore, as a fuel cell including a stack structure formed by stacking a plurality of solid oxide fuel cell units, there is one disclosed in U.S. Pat. No. 6,344,290.
In the case of this fuel cell, both gases which are fuel gas and air are supplied thereto from center portions of cell plates and to be discharged from outer peripheral portions of the cell plates. Accordingly, unburned gas cannot be collected. As a result, when a gas flow is changed at such a time when the fuel cell is under transient operation, a fuel utilization drops to decrease a coefficient thereof. In addition, combustion of the fuel in the outer peripheral portions becomes unstable. Therefore, there is an apprehension that a local thermal stress is applied to each cell, causing a breakage thereof.
In this connection, as a fuel cell composed in order to solve such an apprehension as described above, there is one described in Japanese Patent Unexamined Publication No. 2004-207028.